Welded miter joints with square lapped joints



June 25, 1957 .1. c. GRANFIELD 2,797,396

WELDED MITER JOINTS WITH SQUARE LAPPED JOINTS Filed March 27, 1951 I 2 Sheets-Sheet 1 Inventor:

by W

His Attorneg.

John C. Stanfield,

J1me- 1957 J. c. GRANFIELD WELDED MITER JOINTS WITH SQUARE LAPPED JOINTS Filed March 27. 1951 2 Sheets-Sheet 2 ITS/enter; John C. Granfield,

His Att orn e g.

United States Patent WELDED MITER JOINTS WITH SQUARE LAPPED JOINTS John C. Granfield, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application March 27, 1951, Serial No. 217,831

1 Claim. (Cl. 336-217) This invention relates to magnetic cores for stationary electrical induction apparatus and more particularly to a laminated magnetic core having welded miter joints and to a method of constructing such a magnetic core.

. During recent years there has been widespread growth in the electrical industry of the use of oriented magnetic steel for the construction of magnetic cores. For example, cold rolled silicon strip steel has decided magnetic advantages when the strips of magnetic material are so oriented with respect to the magnetic core structure that the normal path of magnetic flux travel is in the direction of the grain of the strip steel material.

It has been found that one of the major causes of core loss in magnetic cores constructed of fiat stacked oriented strip magnetic material occurs at the corners of the core where the flux must change direction in turning the corner between intersecting laminations and travel across the grain of the magnetic material. Efforts have been made to devise constructions which will reduce this core loss at the corners of the core. For example, mitered joints have been used at the intersection of laminations, with each of the intersecting laminations being diagonally cut at the corners to provide the mitered joint. However, mitered joints of the type just described have the disadvantage that there is very little overlap between laminations of adjacent layers, with the result that such mitered joint constructions are not as satisfactory from a mechanical or structural standpoint as the conventional butt and lap construction using rectangular laminations. In addition, cores having such mitered joints are not as readily assembled as the conventional butt and lap construction using rectangular-shaped laminations.

It is an object of this invention, therefore, to provide a new and improved magnetic core construction which will reduce magnetic core losses at the core corners as compared to corners having a conventional butt and lap construction.

It is a further object of this invention to provide a magnetic core construction having the magnetic advantages of a miter joint construction but with the mechanical strength and ease of assembly characteristic of conventional butt and lap lamination arrangements.

It is a still further object of my invention to provide a new and improved method for constructing magnetic cores of the type using oriented magnetic material.

In accordance with these objectives, my invention provides a new and improved magnetic core and a method of constructing such a core in which rectangular members of strip magnetic material are diagonally cut at degrees at the corners, with the cut corner piece being reversed and welded back into position in such manner as to provide proper magnetic orientation at the corners of the strip, still preserving the rectangular shape of the strip. Such strips may then be assembled in the conventional butt and lap method of assembly.

The features of this invention which I believe to be novel are set forth with particularity in the appended "ice claims. My invention itself, however, both as to its organization and use, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 represents a generally rectangular-shaped single phase magnetic core constructed in accordance with my invention; Fig. 2 represents one of the strip members of the core of Fig. 1 before the cutting and welding operation is performed; Fig. 3 represents the strip of Fig. 2 after the corner member has been cut and welded back into position; while Fig. 4 represents a three-phase magnetic core constructed in accordance with my invention.

Referring now to the drawing, there is shown in Fig. l a generally rectangular-shaped magnetic core 1 having leg members with outermost laminations 2 and 3 and yoke members with outermost laminations 4 and 5. Each of the layers of the magnetic core 1 comprises four rectangular shaped laminations, such as 2, 3, 4, and 5, including two leg laminations and two yoke laminations. The core is constructed of strip magnetic material in which the grain of the magnetic material is oriented in the same direction as the path of magnetic flux travel. In accordance with my invention, in order to provide proper orientation of the magnetic material at the corners of the core, the rectangular strips which constitute the core have had their corners cut diagonally at an angle of 45 degrees, with the cut corner member subsequently being butt welded to the strip from which it was cut in such manner as to provide proper orientation of the magnetic material at the corners, as will be hereinafter described.

The outermost leg lamination 2 has butt welded to it a corner member 6. Corner member 6 is the original corner of lamination 2 but has been turned over or reversed and then butt welded back into position again. The eifect of this is to align the grain of member 6 at right angles to the grain of member 2, thereby providing the proper orientation for the magnetic flux which turns the corner between the intersecting laminations 2 and 5. It will be noted that lamination strip member 2 and corner member 6 after being welded constitute a unitary rectangular-shaped member for purposes of assembly.

' Similarly, lamination 5 is rigidly attached to corner member 7, lamination 3 is rigidly attached to a corner member 8 and lamination 4 is rigidly attached to a corner member 9. Thus, it will be seen that the outermost layer of core 1, as just described, is made up of four rectangularshaped members which may be assembled with the other layers of the core in a conventional butt and lap method of assembly. Yet the four rectangular-shaped members comprising each layer of core 1 are each formed by joining together two members with a butt weld, these two members including the corner insert member cut at a 45 degree angle from the corner of each strip, and the strip from which it is cut. Thus, strip 2 and corner 6 comprise a rectangular-shaped strip member. Similarly, strip 5 and corner 7, strip 3 and corner 8, and strip4 and corner 9 each constitute a pair. of members which together form a unitary rectangular-shaped strip.

Referring now to Fig. 2, there is shown a strip of oriented magnetic material illustrating the manner in which the corner members are cut. It will be noted that the cut 10 is made at a 45 degree angle at the corner of the strip member. The corner member 11 is then reversed and butt welded back into position as shown in Fig. 3. Thus, the orientation of the grain of the magnetic grain in the reversed insert member 11 as shown in Fig. 3 is perpendicular to the direction in the main body of the strip 12.

My rectangular laminations with welded miter joint corners may be used in any type of core which may be constructed of rectangular-shaped laminations. As another example of a core which may be constructed using rectangular welded strips in accordance with my invention, there is shown in Fig. 4 a three-phase core formed of my welded strips. The core in the particular embodiment illustrated in Fig. 4 is constructed of alternate layers which have been identified by the numbers 13 and 14, respectively. It will be noted that three leg members are provided in each layer, the leg members being connected together at their ends by yoke members. For example, layer 13 is provided with three leg members 15, 16, and 17 which are respectively provided withcorner members 18, 19, and 20. In addition, two short rectangular-shaped members 21 and'22 cover the space from the outer edges of the core to the center leg. Members 21 and 22 are also each provided with corner insert members 23 and 24, respectively. A simple unwelded lamination 25 spans the space from the inner edge of the leg 15 to the inner edge of leg 17.

The outer layer 14 is essentially a top-and-bottom reversal of layer 13 and comprises leg members 26, 27, and 28, each having a corner member welded thereto, respectively numbered 29, 30, and 31. Short strip members 32 and 33 respectively join the outer edge of leg 26 to centerleg 27 and the outer edge of leg 28 to center leg 27. Members 32 and 33 are provided with corner members 34 and 35 respectively. A short unwelded rectangular-shaped strip member 36 connects the inner edges of legs 26 and 28. Layer 14 is essentially a reversal of layer 13 in so far as relative positions of the various members are concerned in order to provide a lapped effect between these adjacent layers. Thus, while outside leg members 15 and 17 of layer 13 abut the bottom edge of the core, with respect to the view shown in the drawing, outside leg members 26 and 28 of layer 14 abut the top edge of the core. Similarly, center leg 16 of layer 13 abuts the top edge of the core while center leg 27 of layer 14 abuts the bottom edge of the core. Similarly, short connecting members 21 and 22 of layer 13 which connect the outer legs to the center leg are at the top edge of the core in layer 13 whereas the corresponding members 32 and 33 are at the bottom edge of the core in layer 14. Also, member 25 of layer 13 which connects the two outer legs 15 and 17 together is at the bottom edge of the core in layer 13 whereas the corresponding member 36 of layer 14 is at the top edge of the core.

In order to obtain a balanced reluctance effect at the mitered joint of the center leg, so that magnetic flux can pass from the center leg with equal ease both to the right and left into the yoke section, it is preferable to provide alternate layers which have their right-left orientation reversed with respect to the layer arrangement shown in Fig. 4. That is, it is preferable to use a four-step layer arrangement in which the first and second layers are similar to layers 13 and 14 and the third and fourth layers are respectively similar to layers 13 and 14, except that the left-and-right orientation of the respective layers is reversed. The same balanced effect can be obtained by making layers 13 and 14 the first and third steps, respectively, in a four-step layer arrangement, and having the second and fourth steps, respectively, left-and-right reversals of layers 13 and 14. By thus reversing the leftand-right orientation as just described, the direction of the miter joints in the center leg members will be reversed in two out of every four layers from the direction shown in layers 13 and 14. The left-and-right reversal hereinbefore described will not affect the direction of the miter joints in the outer legs of the core.

It can be seen that I have provided a new and improved magnetic core construction in which the corners of the individual laminar strips are constructed in such manner as to provide a minimum of core loss at the corners, this improved magnetic characteristic being due to the reorientation of the magnetic material to conform with the natural path of the magnetic flux. By diagonally cutting the corners of the laminar strips at 45 degrees, reversing the cut corner members, and butt welding the cut corner members to the original strip from which'they were cut,'a resultant rectangular strip results which may be assembled with other strips in'a conventional butt and lap method of assembly.

Although I have shown the cut and rewelded corner members reassembled to the respective strip members from which they were cut, obviously corner members cut from similarly-oriented strips are interchangeable.

'While there have been shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that changes and modifications can be made therein without departing from the invention and, therefore, it is aimed in the appended'claim to cover all such changes and modifications as fall within the true spirit andscope of the invention.

What I claim as new and desire to' secure by Letters Patent of the United States is:

A'magnetic core comprised of at least two parallel leg members joined at their respective ends by a pair of yoke members, said members each being comprised 'of a plurality of layers of flat stacked rectangular shaped strips ofmagnetic material, the strips in each member being butt joined to strips in the same respective layer ofadjacent members, the joints betweenstrips of adjacent members being lapped in successive layers, each of said strips being comprised of a first portion having a' grain orientation substantially parallel to the longitudinal edges ofsaid strip, at least one end of said first portion having a second portion in the form of a right triangle butt welded thereto'to complete the rectangular configuration of said strip, said second portion having its grain oriented substantially perpendicular to the grain orientationof. the first portion to which said second portion iswelded, each of said second portions being disposed to form a. joint with the end of an adjacent strip and have a. grain orientation substantially parallel to the 'longtiudinal edges of said adjacent strip.

References Cited in the file of this patent' UNITED STATES-PATENTS 1,783,063 Vienneau "a Nov.. 25,1930 1,805,534 'Troy- 'May 19,1931 2,087,906 Gaston July 27, 1937 2,330,824 Granfield Oct. 5, 1943 2,393,038 Forbes Jan. 15, 1946 

